docs: def get_unresolved(aln_df):
      """Get a list of residue numbers (in the original sequence's numbering) that are unresolved
  
      Args:
          aln_df (DataFrame): Alignment DataFrame
  
      Returns:
          list: Residue numbers that are mutated
  
      """
      unresolved_df = aln_df[aln_df['type'] == 'unresolved']
      unresolved = []
      if not unresolved_df.empty:
          unresolved_df['id_a_pos'] = unresolved_df['id_a_pos'].astype(int)
          unresolved = unresolved_df.id_a_pos.tolist()
      return unresolved